Frequency synthesizers play a key role in a variety of technology industries. For example, frequency synthesizers are implemented in a variety of communication devices such as AM/FM radio, digital cellular phones, two-way subscribers, and spread spectrum transceivers, to name a few. In general, frequency synthesizers control the generation of local oscillator signals and the modulation of transmission signals in a wireless communication device. A frequency synthesizer is used to reliably produce frequencies that are derived from a reference frequency input source.
A fractional-N synthesizer produces output frequencies that are fractional multiples, i.e., integer plus fractional value, of a frequency derived from a reference input source. Fractional-N synthesizers may exhibit non-linear behavior resulting in the generation of undesirable spectral components in the vicinity of a VCO frequency signal, such as the presence of in-band spurs due to the non-linearities of synthesizer components such as but not limited to the phase detector and charge pump.
Thus, there is a need for a method and apparatus for reducing spurs in the fractional-N synthesizer to obtain a VCO frequency signal with reduced spurs.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.